miércoles, abril 14, 2010


M. Fernanda Salinas, Mary T. K. Arroyo and Juan J. Armesto


Three monotypic and endemic genera of epiphytic Gesneriaceae (Gesnerioideae, Coronanthereae) occur in temperate rainforests of southern South America. In this article, intraspecific differences in rooted substrate and interspecific variation in epiphytic growth habits among these three Gesneriaceae species were assessed. The presence or absence of plants on the ground and main rooted substrate when growing epiphytically on trees were used to characterize epiphytic growth habits in two old-growth temperate rainforests of northern Chiloe´ Island in Chile. An evolutionary interpretation based on reported phylogenies and morphologies within the Coronanthereae is proposed. Two species of Chilean Gesneriaceae, Mitraria coccinea Cav. and Asteranthera ovata (Cav.) Hanst., originate from the forest floor, then climb on trees while maintaining their main roots in the ground, and are classified as secondary hemiepiphytes. The third species, Sarmienta repens Ruiz & Pav., was found exclusively on tree trunks and branches of living and dead trees and thus may be classified as a holoepiphyte. Based on reported phylogenies and biogeographical, ecological, and morphological data, the mechanically independent arboreal habit appears to be the ancestral condition in the Coronanthereae, which in turn gave rise to the climbing habit and finally the holoepiphytic habit. This may be a common evolutionary pathway toward holoepiphytism within other lineages in the Gesneriaceae.

lunes, abril 05, 2010

Behavioral development not Genetic Kin Selection!...may explain origins of sociality

It has been proposed that one of the traits that are involved in the origin of sociality is the tolerance among individuals belonging to the same species. This means that the transition from solitary to social life requires the regulation of aggressiveness and the evolution of intraspecific recognition. This is also known as kin recognition, now, when we look at the ideas to explain the origin and maintenance of this trait, there are some contrasting approaches.

The sociobiological school, propose that individuals bearing the same genes may be able to recognize themselves, this correspond to an evolutionary adaptation that allow them to collaborate and keep cohesion of related group of individual. This idea has flourished in the field of behavioral ecology and the mainstream neodarwinian culture, it has been suggested even to explain altruism in humans. However, despite the benefits suggested on the theoretical models for a genetic kin selection, these proposals are often not supported with explanatory mechanism for the occurrence of such kin recognition.

Alternatively to this approach, it have been suggested that the recognition and acceptance of individuals belonging to a defined group correspond to an emergent property due to behavioral development, where the signals present during the construction of the kin fidelity responses are molded by the available cues, these cues can originated either in the group (kin reference) or even derive from the organism itself that is developing its responses (self reference).

One suitable system to study the jump from solitary to social life and the origin and maintenance of intraspecific recognition is constituted by the Xylocopinae (Hymenoptera: Apidae). This group is held as the sister group for all other Apidae subfamilies, and thus it may very likely be the less derived. In addition it contains species that goes from solitary to social life in relation to nesting behavior. Among the solitary species some exhibit features more often present in social species, some of these are related to parental care, contact between related individuals and also tolerance between nestmates. Manueli apostica is one of these solitary bees, it belong to the monogenerial tribe Manuelini inside Xylocopine, a group mainly presented on continental Chile. In these bees, female construct nests inside the dead stem of Chusquea quila (Poaceae: Bambuseae), in these developing offspring are isolated by the mother in single compartments together with food supplies (Figure 1).

In this group, Dr. Luis Flores-Prado and collaborators from Facultad de Ciencias, Universidad de Chile,  have found that the recognition of nestmates individuals and tolerance is either developed from cues present on food masses and nest material provided by the mother or on cues acquired by the insect themselves, also known as self referencing (Experiment 1, Figure 2). In a newly published research Dr Flores-Prado and co. performed a recognition test between two non-kin individuals (a foster and a non manipulated one, Experiment 2, comparison A) developed in the same nest, thus they will experience the same breeding environment.

Furthermore, they compared between two kin females developed in different nest, which were not used as sources of other test (Experiment 2, comparison B). So, this means same kin different environment.

These transplant design allow them to disentangle if kin recognition is achieved due to the cues from food provisioning or from cues that the bee obtain from itself. These experiments demonstrated that non-kin females developed in the same nest were more intolerant (and less tolerant) with each other than kin females developed in different nests (Figure 3). Thus, kin recognition was occurring. Individuals of M. postica are physically isolated while developing up to the adult stage prior to the destruction of cell partitions, and there is no direct contact between them and their mother after oviposition. In addition, non-volatile compounds (such as cuticular hydrocarbons) mediate nesmate recognition in this specie (at has been demonstrated by Dr. Flores-Prado). Based on these evidences the authors suggest that cues used in this “kin” recognition do not correspond to an especially unique kin cues and that kin recognition in this bee specie has occurred through self-referent phenotype matching. Just in the same way chicken embryos are able to develop its how-to-peek on a spot behavior due to the cues derived from the movements of their own organs inside the egg, one of the many amazing examples of behavioral developments discovered by Z.Y. Kuo in the beginning of the XX century. 

Cristian Villagra 


Flores-Prado L Chiappa E & Niemeyer HM Nesting biology, life cycle, and interactions between females of Manuelia postica, a solitary species of the Xylocopinae (Hymenoptera: Apidae). 35:93-102.

Flores-Prado, L. Aguilera-Olivares D. & Niemeyer H.M. 2008 Nest-mate recognition in Manuelia postica (Apidae: Xylocopinae): an eusocial trait is present in a solitary bee. Proc. R. Soc. B 275, 285–291.

Flores-Prado L & Niemeyer HM 2010 Kin Recognition in the largely Solitary Bee, Manuelia postica (Apidae: Xylocopinae). Ethology 115:1–6.

Hamilton, W. D. 1964a The genetical evolution of social behavior, I. J. Theor. Biol. 7, 1–16.

Hamilton, W. D. 1964b The genetical evolution of social behavior, II. J. Theor. Biol. 7, 17–52.

Mateo, J. M. 2004: Recognition systems and biologicalorganisation: the perception component of social recognition.Ann. Zool. Fenn. 41, 729-745.

Michener CD 2000. The bees of the world. Baltimore, Maryland, The John Hopkins University Press. 913 p.

jueves, febrero 25, 2010

A pergunta que Einstein fez à Biologia

A Biologia inteira é muito grata à iniciativa de se personificar processos em moléculas. Chegamos até aqui empurrados pelo valor prático de se tratar o organismo como algo composto de partículas muito bem definidas que podem ser isoladas dos processos que participam e estudadas minuciosamente. Tratamos a herança como transmissão de partículas e cá estamos na era pós-genomica. Mas, a despeito do genoma humano, não entendemos muito bem sobre os processos gerativos e conservativos do viver. Neste contexto, quero aqui relembrar uns experimentos antigos que são seríssimos e depois quero terminar com a pergunta que Einstein fez à Biologia.

Entre as salamandras Triturus viridescens é comum a ocorrência, natural ou induzida, de poliploidia. Particularmente, o embriologista Frankhauser trabalhava na década de 40 com salamandras que podiam ser haplóides, diplóides ou pentaploides. Era uma situação muito curiosa porque existe uma relação muito linear entre o número de cromossomos e o volume celular: as células que tinham 5 vezes o número de cromossomos eram realmente muito maiores que as células haplóides. Entretanto, e aí está o curioso, Frankhauser observava que as salamandras pentaplóides ou haplóides tinha os órgãos e o corpo com o mesmo tamanho que as salamandras haplóides. Isso acontecia devido às compensações no número de células que compunham cada um dos órgãos. A figura mais conhecida deste trabalho eu mostro abaixo, que trata do diâmetro dos ductos pronéfricos. Percebam que interessante, não importa o tamanho das células, o diâmetro dos ductos pronéfricos é conservado o mesmo porque nas salamandras haplóides esses ductos são feitos de 6-8 células, mas nas salamandras pentaplóides eles são constituídos de 1-2 células. Mudam os componentes, segue conservada a forma. A condição sistêmica grita forte nesse caso!

Agora vejam que interessante: logo depois de publicar este artigo em 1945, Frankhauser recebeu uma carta do físico Albert Einstein com a seguinte colocação:

" It is really marvel, the living being. The fact alone that the thing can exist with the three or four fold crhomosome number is extremely remarkable. Most peculiar, however, for me is the fact that, in spite of the enlarged single cell, the size of the animal is not correspondingly increased. It looks as the importance of the cell as rulling element of the whole had been overestimated previously. What the real determinant of form and organization is seems quite obscure."

Parece que os problemas biológicos ficam mais claros para quem está de fora da Biologia. Que resposta temos a oferecer a Einstein, tanto tempo depois?


Frankhauser (1945) Maintenance of normal structure in heteroploid salamander larvae, through compensation of changes in cell size by adjustment of cell number and cell shap. J Exp. Zool.00(3) pags. 445-455